On-load tap changers serve, as is known, for uninterrupted switching between different winding taps of a tapped transformer and thus for voltage regulation. They usually consist of a selector for power-free selection of that winding tap of the tapped transformer that is to be switched to as well as a load-changeover switch for the actual uninterrupted switching from the previously connected winding tap to the new, preselected winding tap. The load-changeover switch has for that purpose the components required for such an uninterrupted rapid switching, particularly a force-storing unit, a drive shaft, switching contacts—these can be mechanical switching contacts, vacuum switching cells or also thyristors—as well as means for actuation of the switching contacts in a predetermined switching sequence for each changeover process.
Known load-changeover switches usually additionally have an individual oil vessel, usually in the form of a closed insulating-material cylinder in which all mentioned components are located separately from the surrounding oil of the transformer. Arranged to be located directly below the load-changeover switch, but in the transformer oil, is the selector, which is connected with the central drive shaft of the load-changeover switch by way of a transmission stage. The central drive shaft of the load-changeover switch is driven by way of a motor drive, which is outside the transformer housing and that slowly draws up the force-storing unit by a linkage—that is similarly led along the transformer housing at the outside—and in that case also simultaneously actuates the selector. The central drive shaft is thus responsible not only for actuation of the switching contacts of the load-changeover switch during the actual rapid switching, but also for actuation of the selector, which is directly below the load-changeover switch, during the slow drawing-up process of the force-storing unit.
On-load tap changers of that kind are products established for decades on the market and are known from, for example, the company publication of the applicant “Oiltap® M Laststufenschalter fur Regeltransformatoren.” Shown on page 1 of the company publication is an on-load tap changer of the kind according to category, which has in the upper region, within the insulating cylinder, a load-changeover switch and directly adjacent thereto the selector, which is connected by way of a transmission stage with the drive shaft of the load-changeover switch. Not shown in this illustration is the force-storing unit and the motor drive in operative connection therewith by a linkage.
This described construction, which has been current for many years in the prior art, is, however, space-consuming for transformer constructors, since it takes up a relatively large amount of space within the transformer housing and thus limits the degree of freedom of the transformer manufacturer in the construction of the actual transformer in the transformer housing, which is confined in terms of space. This is not least because a relatively large space has to be left free within the transformer housing for location of the placement of the on-load tap changer and this space still cannot be flexibly designed for the purpose, but is quasi predetermined by the construction of the on-load tap changer, consisting of load-changeover switch and selector directly thereunder, known from the prior art.
The company publication “Stufenschalter Typ G” of the applicant in that case reveals a typical arrangement of an on-load tap changer according to category in the configuration, i.e. in the combination, of tap changer and regulating transformer. As apparent from the cover sheet, an on-load tap changer of that kind, thus load-changeover switch and associated selector, is at a specific dielectric spacing from the individual windings of the transformer within the transformer housing and from the walls of the transformer housing. In that case, apart from the on-load tap changer, consisting of load-changeover switch and selector directly adjoining underneath, the installation of the individual dielectrically insulated copper lines from the corresponding winding taps of the regulating winding of the transformer to the respective selector contacts requires a substantial amount of space. The line guidance, which is fastened to the transformer active part by the shunt equipment is, however, not only time-consuming in its installation, but also due to the requisite electrically conductive characteristics thereof made of copper and thus very expensive.